The present invention relates generally to Q-switched microresonators and, more particularly, to densely packed microlaser assemblies including Q-switched microresonators.
Modern electro-optical applications are demanding relatively inexpensive, miniaturized lasers capable of producing a series of well-defined output pulses. As such, a variety of microlasers have been developed that include a microresonator and a pair of at least partially reflective mirrors disposed at opposite ends of the microresonator to define a resonant cavity therebetween. The microresonator of one advantageous microlaser includes an active gain medium and a saturable absorber that serves as a Q-switch. See, for example, U.S. Pat. No. 5,394,413 to John J. Zayhowski which issued on Feb. 28, 1995 and U.S. Pat. No. 6,072,815 to Brian L. Peterson which issued on Jun. 6, 2000, the contents of both of which are incorporated in their entirety herein. By appropriately pumping the active gain medium, such as with a laser diode, the microresonator will emit a series of pulses having a predetermined wavelength, pulse width and pulse energy.
Conventional microlasers, such as those described by U.S. Pat. No. 5,394,413,are end pumped in a direction parallel to the longitudinal axis defined by the resonator cavity. In this regard, the longitudinal axis of the microresonator cavity extends lengthwise through the resonator cavity and is oriented so as to be orthogonal to the pair of at least partially reflective mirrors that define the opposed ends of the resonant cavity. As such, conventional microlasers are configured such that the pump source provides pump signals in a direction perpendicular to the at least partially reflective mirrors that define the opposed ends of the resonant cavity. The effective length of the resonator cavity is therefore equal to the physical length of the resonator cavity.
In order to increase the pulse energy and the average power of the laser pulses, the resonator cavity of a microlaser is preferably lengthened. While a microlaser can be fabricated such that the resonator cavity has different lengths, a number of factors contribute to generally limit the permissible length of the resonator cavity. In particular, a number of electro-optical applications require microlasers that are extremely small. In addition, the length of passively Q-switched microlasers is effectively limited by the requirement that the inversion density must exceed a predetermined threshold before lasing commences. As the physical length of the resonator cavity increases, greater amounts of pump energy are therefore required in order to create the necessary inversion density for lasing.
In order to effectively increase the length of the resonant cavity without increasing its physically length, side-pumped microlasers have been developed as described by U.S. patent application Ser. No. 09/337,432, filed Jun. 21, 1999, by Brian L. Peterson, et al. and U.S. Pat. No. 6,219,361, issued Apr. 17, 2001 to Steve Guch, Jr., et al., the contents of both of which are incorporated in their entireties herein. Like an end-pumped microlaser, a side-pumped microlaser includes a microresonator consisting of an active gain medium and a saturable absorber that serves as a Q-switch, and a pair of at least partially reflective mirrors disposed at opposite ends of the microresonator to define a resonant cavity. Unlike an end-pumped microlaser in which the opposed end faces of the microresonator are perpendicular to the longitudinal axis defined by the microresonator, however, the opposed end faces of the microresonator of a side-pumped microlaser are disposed at a non-orthogonal angle, such as between about 30xc2x0 and about 35xc2x0, relative to a line perpendicular to the longitudinal axis defined lengthwise through the microresonator. As such, the microresonator will support a zig-zag resonation pattern. In order to initiate the resonation, the microlaser also includes a pump source for introducing pump signals into the active gain medium via a side surface of the microresonator. In response to the pumping of the active gain medium via the side surface, the zig-zag resonation pattern is established within the resonant cavity and a series of pulses are emitted once the necessary inversion density has been reached. As a result of the zig-zag resonation pattern, the effective length of the microresonator of a side-pumped microlaser is increased without having to increase the physical dimensions. Thus, a side-pumped microlaser can generate pulses having greater pulse widths and correspondingly greater pulse energies and average power levels than the pulses provided by end-pumped microlasers of a similar size.
Notwithstanding the advantages offered by side-pumped microlasers, some modern electro-optic applications require pulses that have greater pulse energies and greater average power levels as well as pulses that have different frequencies or wavelengths than those emitted by a microresonator. As such, microlaser assemblies can include one or more electro-optic components in addition to microresonator for receiving and modifying the pulses. For example, the electro-optic components can include an optical parametric amplifier or an optical parametric oscillator. Alternatively, the electro-optic optic components can include one or more non-linear crystals for altering the wavelength of the pulses, such as by doubling or quadrupling the frequency of the pulses.
While the additional electro-optic components modify the pulses emitted by microresonators so as to have the desired amplitude, frequency or other signal characteristics, the addition of the electro-optic components increases the size of the resulting microlaser assembly. With many electro-optic applications, it is desirable to minimize the size of the microlaser assembly. As such, it would be advantageous to configure the microresonator and the other electro-optic components of the microlaser assembly as densely as possible. This dense packing of the components of a microlaser assembly presents additional challenges, however, including the accurate alignment of the microresonator and the electro-optic components and the thermal management of the components. In this regard, the dense packing of the components can exacerbate the loss or other attenuation caused by misalignment. In addition, the heat generated by the plurality of closely packed electro-optic components is generally more concentrated and must be transferred to a heat sink, a thermoelectric cooler or the like in order to maintain the electro-optic components at a predetermined operating temperature.
A wedge-shaped microresonator is therefore provided that can be mounted proximate one or more electro-optic components in order to construct a densely packed microlaser assembly. The microresonator includes at least a pair of converging side surfaces that define an acute angle therebetween. In this regard, the wedge-shaped microresonator has first, second and third side surfaces. The wedge-shaped microresonator includes an active gain medium having a wedge shape and a passive Q-switch proximate at least one side surface. For example, the passive Q-switch may be proximate the second side surface and the active gain medium may be proximate portions of the first and third side surfaces. The wedge-shaped microresonator also includes a reflective surface proximate each of the first, second and third side surfaces. At least one of the reflective surfaces, typically the reflective surface that is proximate the second side surface, i.e., proximate the passive Q-switch, is partially reflective to permit emission of laser signals.
In addition to the wedge-shaped microresonator, a microlaser assembly according to one aspect of the present invention also includes at least one electro-optic component for receiving and modifying the laser pulses emitted by the wedge-shaped microresonator. In one advantageous embodiment, both the microresonator and the at least one electro-optic component are wedge-shaped. As such, the microresonator and the electro-optic component(s) may be arranged in a ring-like configuration. As a result of the wedge-shape of the microresonator and the electro-optic components, the microlaser assembly can be packed relatively densely. Moreover, the wedge shape of the components of the microlaser assembly facilitates the precise alignment of the microresonator and the other electro-optic components. In one embodiment, the microlaser assembly further includes an auxiliary electro-optic component for receiving an output from either the microresonator or another electro-optic component. The auxiliary electro-optic component may be radially offset from the ring-like arrangement of the microresonator and the electro-optic component(s). The microlaser assembly may include a wide variety of electro-optic components including optical parametric oscillators, optical parametric amplifiers, frequency altering components, such as frequency doubling crystals or the like, gain switched resonators and active gain mediums.
Regardless of whether the microlaser assembly includes other electro-optic components, the microlaser assembly generally includes a pump source for providing pump signals to the microresonator. In one advantageous embodiment, the pump source includes a plurality of pump sources arranged to pump the microresonator in a triangular pattern. In this regard, the plurality of pump sources may be arranged such that the triangular pattern extends between medial portions of the first, second and third side surfaces of the microresonator. In addition, the microresonator and the pump sources can be mounted upon a heat sink that serves to maintain the temperature of the microresonator and the pump sources within a predefined range during operation of the microlaser assembly. In one embodiment, for example, the heat sink is positioned between the pump sources and the microresonator. In this exemplary embodiment, the heat sink defines at least one opening therethrough such that the pump sources may be positioned relative to the heat sink so as to provide pump signals through respective openings to the microresonator. For example, the heat sink may define openings in the triangular pattern in which the microresonator is to be pumped. Regardless of the particular configuration, the microlaser assembly including the wedge-shaped microresonator of the present invention can be reliably operated to produce laser signals having the desired signal characteristics, while also permitting the components to be densely packed.